1. Technical Field
The present invention relates generally to submicroscopic structures and more particularly to sub-microscopic wires and openings.
2. Background Art
In many fields, especially biology and electronics, it has become important to be able to form smaller and smaller openings and electrical wires in order to be able to advance the technology by providing smaller and more sensitive devices.
For example in biology, it has become important to be able to study single-stranded DNA and RNA in various fields, such as medicine and biological research. By studying DNA and RNA, various diseases can be detected and treated.
Unfortunately, the individual components of the DNA and RNA are nano-scale structures (10−9 meter and below), which are sub-microscopic and cannot be identified directly. For example, a single-stranded DNA is made up of a number of components called “nucleotides”, which are designated by the letters A, C, G, and T (for adenine, cytosine, guanine, and thymine). The human genome is about 3.2 billion nucleotides long, which is analogous to a million-page book having different length words and 3,200 letters per page.
In order to be able to identify a single-stranded DNA or RNA, it is necessary to be able to process one strand at a time. Unfortunately, there is currently no method that allows a direct measurement of one strand or even a method to line up the single strands in such a way that the strands may be identified.
The ideal would be to electronically sense biological polymers, like RNA, DNA, and proteins, and also unlabeled polynucleotides at a molecular level so as to be able to characterize individual molecules with regard to length, type, and sequence. This would be accomplished by passing a strand of molecules through an opening in a film and electronically sensing the molecules. In addition to a problem forming the electrodes for the electronic sensing, the major problem has been with making an opening small enough that only one strand of molecules would pass through.
Methods used in the past for creating the required opening included both organic and inorganic techniques.
In an example of an organic technique, a lipid bilayer membrane would be stretched across a 30-μ hole in a piece of PTFE (such as Teflon(TM)) separating two compartments filled with buffer fluids. Molecules of a protein, α-hemolysin, would be added to one of the buffer-filled compartments and the α-hemolysin would interact with the lipid bilayer membrane for five minutes. Generally, an ion channel would form in the membrane, after which the remaining α-hemolysin was immediately flushed out to prevent other openings from forming. However, there were a number of problems including drifting of the opening due to the fluid nature of the membrane, the instability of the opening due to surrounding conditions (such as pH, temperature, etc.), and the inability to adjust the size of the opening.
In an example of an inorganic technique, a freestanding silicon nitride film was sputtered using a focused ion beam (FIB) to create an initial opening in the film. A low energy argon ion beam was then used to melt the film around the initial opening to close or open the opening to a desired size. This has also been problematic due to the difficulty of controlling the material at the final perimeter of the opening to provide circular openings. Often the openings would be somewhat irregularly shaped and not completely circular. Further, the processes often were not predictable, not robust, and/or were time-consuming for forming single openings even when successful.
Another problem with the prior art related to providing the openings with probe electrodes, which would allow electrical sensing of molecules in the opening. Previously, there was no method for providing small enough metallic probes for the small openings or for properly locating metallic probes with respect to the small openings. This problem correlates with problems in the electronics field generally.
For example, in electronics, it is desirable to have smaller and smaller structures to conduct electricity. This is both to be able to reduce the size of electronic devices such as microprocessors, as well as to be able to place them closer together to speed up operation. Present day wires and structures used in devices such as microprocessors are 100 nm meter in size and this small size still is so large that it limits how small the devices can be manufactured. Smaller devices have many advantages including higher speed, lower cost, and lower power requirements.
Solutions to these problems have been long sought, but have long eluded those skilled in the art.